The present invention relates to rubber-modified blends of two polymers, one or both of which are rubber-modified. One polymer contains a vinyl aromatic monomer such as styrene or p-methylstyrene, and an unsaturated dicarboxylic acid anhydride such as maleic anhydride. It may optionally contain up to 25 percent of a third monomer such as acrylonitrile, methacrylonitrile, or methyl methacrylate and may also optionally contain 5 to 30 percent of a rubber grafted with a portion of the copolymer. The other polymer is a methyl methacrylate homopolymer, or a methyl methacrylate copolymer containing up to 30 percent of a vinyl aromatic monomer or up to 20 percent of an alkyl acrylate. This polymer may optionally contain 10 to 60 percent of a rubber grafted with a portion of the polymer.
To the blend may be added, (a) 10 to 60 percent of a vinyl chloride resin, which may optionally contain 2 to 30 percent of a rubber grafted with less than 50 percent of the polymerized vinyl chloride, (b) up to 20 percent of an ungrafted rubber, or (c) up to 40 percent of a graft copolymer of rubber, styrene, and acrylonitrile, methacrylonitrile, or methyl methacrylate or a mixture thereof.
Copolymers of styrene and maleic anhydride (S/MA) are known to have high softening temperatures and have been blended with various resins which have lower softening temperatures than those of the S/MA copolymers in order to provide higher softening temperatures than those of the resin. Better impact strengths were obtained if the copolymers used in the blends were rubber-modified. The resins of such blends included styrene-acrylonitrile copolymers (S/AN), ABS resins (graft copolymers of styrene, acrylonitrile, and rubber, usually butadiene-based), vinyl chloride resins, and methyl methacrylate homopolymers or copolymers containing a small amount of styrene or an alkyl acrylate.
The present invention discloses the preparation of blends in which either component, or both, is rubber-modified by polymerizing the monomers in the presence of one or more rubbers to form a graft copolymer dispersed as a separate phase.
Belgian Pat. No. 767,255 describes polyblends of unmodified S/MA copolymers with methyl methacrylate homopolymers or copolymers containing 4, 6.5, and 7.5 percent of methyl acrylate. Blends containing the two components in a 50:50 weight ratio exhibited Vicat softening temperatures between those of the two components, indicating good compatibility. A blend of a 86.4:13.6 S/MA copolymer with a methyl methacrylate copolymer containing 20 percent of styrene exhibited a Vicat softening temperature of 114.degree. C., compared with 126.degree. and 103.degree. C. for the copolymers, respectively. A blend of a 82:18 S/MA copolymer with a methyl methacrylate copolymer containing 4 percent of methyl acrylate exhibited a Vicat softening temperature of 122.degree. C., compared with 134.degree. and 105.degree. C. for the two copolymers, respectively. A blend of a 76.7:23.3 S/MA copolymer with the same methyl methacrylate copolymer exhibited a Vicat temperature of 125.degree. C., compared with 145.degree. and 105.degree. C. for the copolymers, respectively. Three-component blends, prepared by adding S/AN copolymers containing 20 or 25 percent of acrylonitrile to the blend, had good compatibility, based on Vicat softening temperatures.
Certain copolymers of methyl methacrylate also show good compatibility with vinyl chloride resins. Copolymers containing 5 percent of ethyl acrylate or 10 percent of butyl acrylate were reported to be miscible with polyvinyl chloride. (See Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Volume 18, p. 462, John Wiley and Sons, New York, 1981.)
Copolymers containing a small portion, e.g. 3 to 15 percent, of a lower alkyl acrylate comonomer are frequently used as processing aids for vinyl chloride resins, usually in amounts of 0.5 to 10 parts per hundred of resin. Such copolymers are believed to be compatible with vinyl chloride resins. The homopolymer of methyl methacrylate has been reported to be compatible with vinyl chloride resins. (See Burgess, Manufacturing and Processing of PVC, pp. 98, 237-240, MacMillan, N.Y., 1982, and European Patent Application 53,080, Nov. 23, 1981.)
U.S. Pat. No. 4,434,252 describes blends of vinyl chloride resins containing 0.1 to 15 parts per hundred of resin of homopolymers or copolymers of an alkyl methacrylate, preferably methyl methacrylate, containing up to 25 percent of an alkyl acrylate, in which the alkyl group preferably has 1 to 4 carbon atoms, or up to 20 percent of a vinyl aromatic monomer such as styrene or alpha-methylstyrene. Such blends were used for rigid foam.
As is well-known, many rubber-modified polymers, such as high impact polystyrene or S/MA copolymers containing butadiene-based rubbers, exhibit poor transparency because the refractive index of the matrix is higher than that of the dispersed rubber (or graft copolymer) phase. Blends containing such polymers also normally exhibit poor transparency. As is also well-known, the introduction of non-aromatic monomers such as acrylonitrile, methacrylic acid, methyl methacrylate, and the like into styrene polymers reduces the refractive index, while the introduction of vinyl aromatic monomers, particularly styrene, into rubbers based on 1,3-butadiene or isoprene, increases the refractive index of the graft copolymer phase. Block copolymerization is preferred, particularly if 20 percent or more of styrene is used. Such block copolymers include diblock, triblock, radial, and star-shaped copolymers.
The amount of methyl methacrylate required in the matrix copolymers to impart transparency decreases as the amount of styrene in the rubber increases. British Pat. No. 1,046,646 discloses the synthesis of transparent copolymers of styrene and methyl methacrylate prepared by copolymerizing the monomers in the presence of block copolymer rubbers of 80 to 50 percent of butadiene-1,3 and 20 to 50 percent of styrene. The ratio of styrene to methyl methacrylate was varied from 30:70 to 65:35. U.S. Pat. No. 4,129,615 discloses a transparent rubber-modified copolymer of styrene and methyl methacrylate which contained a block copolymer rubber of butadiene and styrene. U.S. Pat. No. 3,359,345 describes the preparation of transparent copolymers of methyl methacrylate and alpha-methylstyrene polymerized in the presence of a block copolymer of 1,3-butadiene and styrene.
Methyl methacrylate was introduced into graft copolymers containing styrene, acrylonitrile, and a butadiene-based rubber, in order to reduce the refractive index to match that of the graft copolymer phase (Encyclopedia of Polymer Sci. and Tech., Supp. Vol. 1, pp. 307-325, John Wiley and Sons, 1967). Polystyrene has a refractive index of about 1.591, compared with about 1.491 for polymethyl methacrylate and 1.515 for polyacrylonitrile. MBS, graft copolymers of approximately equal amounts of styrene and methyl methacrylate and about 50 weight percent of a butadiene-based rubber, are blended with vinyl chloride resins to produce transparent blends. Such blends are commercially available.
The use of rubber-modified and unmodified S/MA copolymers in blends with other resins, specifically polyvinyl chloride resins, is described in my three co-pending applications, Ser. No. 494,708, now U.S. Pat. No. 4,469,844, and Ser. No. 494,709, now U.S. Pat. No. 4,469,845, both filed May 16, 1983, and Ser. No. 636,961, filed Aug. 2, 1984, the contents of these three applications being incorporated by reference herein. Blends of such S/MA copolymers with other resins, are described in detail in said co-pending applications, and are summarized below.
U.S. Pat. No. 3,642,949 describes blends of S/MA copolymers with S/AN copolymers or ABS resins in order to provide increased softening temperatures. U.S. Pat. No. 4,339,554 describes blends of rubber-modified or unmodified S/MA copolymers with unmodified vinyl chloride resins. U.S. Pat. No. 4,197,376 describes blends of rubber-modified S/MA copolymers or terpolymers containing up to 30 percent of methyl methacrylate (S/MA/MM) or acrylonitrile (S/MA/AN) with ABS resins.
U.S. Pat. No. 3,626,033 describes blends of unmodified S/MA copolymers, unmodified vinyl chloride resins, and ABS. U.S. Pat. No. 4,329,272 describes blends of unmodified S/MA copolymers, which would optionally contain up to 20 percent of methyl methacrylate or acrylonitrile, with unmodified vinyl chloride resins. The blend could optionally contain up to 40 percent of ABS or MBS (a graft copolymer of styrene, methyl methacrylate, and a butadiene-based rubber). U.S. Pat. No. 4,311,806 describes similar blends in which the maleic anhydride copolymers or terpolymers were rubber-modified.
Bourland and Wambach (J Vinyl Technol., 1983, 5 (3), p. 121; Plastics Engineering, May, 1983, p. 23) disclosed that S/MA copolymers are partially miscible with vinyl chloride resins and hence increase the softening temperature and reduce melt viscosity. Impact modifiers could be added to the blends.
Hall, Mendelson, and Trementozzi discussed the preparation of blends of various terpolymers containing maleic anhydride with random S/AN copolymers or ABS. (See Preprint for Organic Coatings and Plastics Chemistry Division, 47, p. 298, Meeting of the Am. Chem. Soc., Sept. 12-17, 1982.)
U.S. Pat. No. 4,454,300 describes blends of a vinyl chloride-polyolefin graft (rubber-modified) copolymer with S/MA copolymers. Preferred polyolefin elastomers were copolymers of ethylene and propylene, or terpolymers containing up to 15 percent of a diene monomer (EPDM). A blend, in a 60:40 weight ratio, of an unmodified S/MA copolymer (containing 14 weight percent of maleic anhydride) with a vinyl chloride resin containing 14 percent of rubber, exhibited a heat distortion temperature of 87.degree. C., compared with 67.degree. C. for the vinyl chloride resin and 105.degree. C. for the S/MA copolymer. The copolymers could contain up to 25 percent of a third monomer such as acrylonitrile or methyl methacrylate, and could be rubber-modified.